This is hidden brain.
I'm Shankar Vedantam.
When you're the parent of a small child, it's not uncommon to have an experience like this.
Your kid comes home from preschool and says, the butterfly flew away.
You go, what butterfly?
And your child looks at you puzzled.
She doesn't realize that the butterfly she saw at preschool when you were not around is not a butterfly you know anything about.
In the minds of very small children, there is no sharp line between what they know and what others know.
But at some point early in childhood, all of us made a magical discovery.
Our thoughts belong only to us.
Parents, siblings, teachers.
No one can enter our minds and see what we are thinking.
A second discovery follows shortly afterward.
If no one can see what is happening inside our minds, we can hide things from other people.
We can keep secrets.
So the pain of keeping this secret.
Has been one of the biggest challenges.
I've had to deal with in my adult life.
I do think constantly about it, and I can't tell anybody about it now.
Because I'm afraid of what might happen.